Cereal smuts in Manitoba and Saskatchewan, 1989-95

Grain yield losses due to the smuts are currently controlled by the application of fungicides to seed and by the use of resistant cultivars. It is important to monitor the natural populations of the six species of cereal smut that affect barley, oat, and wheat to ensure early detection of resistance to fungicides and potentially threatening changes in virulence. Surveys were conducted in farm fields in Manitoba and Saskatchewan from 1989 to 1995 to detect changes in the incidence and severity of these cereal smuts and to make collections that could be screened for carbathiin resistance and virulence. The percentage of fields of barley affected by smuts ranged from 51% in 1992 to 82% in 1995, with the mean percentage of infected plants and thus grain yield losses (with smut diseases of cereals, the percentage of infected plants equates to the percent yield loss) ranging from 0.2% in 1991 to 0.8% in 1989. In oat, the percentage of fields affected by smuts ranged from 2% in 1994 to 23% in 1992, with means of 0.1% or fewer infected plants. The percentage of common bread wheat fields affected varied from 6% in 1989 to 36% in 1995 with means of 0.1% or fewer infected plants. Durum wheats are generally more susceptible and the percentage of fields affected varied from 45% in 1994 to 78% in 1995, with the mean level of infected plants per field ranging from <0.1 to 0.4%. Mean levels of infection of barley, oat, and wheat have declined from 1982-88 levels. None of the more than 1100 collections of the six species of smut from 1989 to 1995 were resistant to carbathiin. The frequency of Ustilago nuda collections virulent on barley cv. Conquest remains high at 41-89%, indicating that genes Un3 and Un6 are of little value now. None of the collections were virulent on line CI 13662, which contains the gene Un8 now being incorporated into Canadian cultivars.